1. Field of the Invention
The present invention relates to a driving and detecting circuit of a vibrator, and particularly to a driving and detecting circuit of vibrator used for a vibrating gyroscope, an acceleration sensor or a pressure sensor using a vibrator.
2. Description of the Prior Art
FIG. 10 is an illustrative view showing a conventional driving and detecting circuit of a vibrating gyroscope which is a background of the present invention. A vibrating gyroscope 1 includes a vibrating body 2 having, for example, a regular triangular prism shape. The vibrating body 2 is formed with a material that generates a mechanical vibration such as elinver. Piezoelectric elements 3a, 3b and 3c are formed on three side faces of the vibrating body 2. The piezoelectric elements 3a and 3b are used for driving a bending vibration to the vibrating body 2, and for detecting a signal corresponding to a rotational angular velocity applied to the vibrating gyroscope 1. The piezoelectric element 3c is used for feedback when the vibrating body 2 is self-oscillated.
An oscillation circuit 4 and a phase correction circuit 5 are connected between the piezoelectric elements 3a, 3b and the piezoelectric element 3c. The piezoelectric elements 3a and 3b are connected to a differential circuit 6. The vibrating body 2 bends and vibrates in a direction perpendicular to a face of the piezoelectric element 3c by applying a signal from the oscillation circuit 4. In this state, signals applied to the piezoelectric elements 3a and 3b are the same signal, and a driving signal component is not obtained from the differential circuit 6. Since the vibrating body 2 bends and vibrates in a direction perpendicular to the face of the piezoelectric element 3c, signals generated in the piezoelectric elements 3a and 3b are the same signal, and the signals generated in the piezoelectric elements 3a and 3b are not obtained from the differential circuit 6. As such, an output signal from the differential circuit 6 is zero, and it is known that the rotational angular velocity is not applied to the vibrating gyroscope 1.
When the vibrating gyroscope 1 rotates on its axis, a vibrating direction of the vibrating body 2 changes by a Coriolis force. A difference is produced between output signals of the piezoelectric elements 3a and 3b by the change in vibrating direction, and the difference of the output signals is obtained from the differential circuit 6. Since an output signal of the differential circuit 6 corresponds to the rotational angular velocity applied to the vibrating gyroscope 1, the rotational angular velocity can be detected by measuring the output signal of the differential circuit 6.
However, when a vibrating gyroscope is used, there is a possibility that a difference of resonance characteristics is produced between two resonance systems including two driving piezoelectric elements by an impedance change of the piezoelectric elements or a frequency change of the driving signal due to, for example, an environmental temperature change. In this case, a difference is produced between driving signals applied to two piezoelectric elements, and a signal corresponding to the difference between the driving signals is obtained from the differential circuit. Thus, an output signal is obtained from the differential circuit even when the rotational angular velocity is not applied, and it causes drift. When the difference is produced between the resonance characteristics of resonance systems, the disturbance is produced in vibrational attitude of the vibrating body. The disturbance appears as the displacement of the vibrating body, and a signal is obtained from the differential circuit even when the rotational angular velocity is not applied, and it causes drift.
In order to cover the disadvantage, methods such as addding a learning function to the circuit or using plural synchronous detecting circuits are considered. However, in these methods, circuit scale becomes large, and the large scale circuit is not extremely satisfactory though it is an excellent method under specific conditions.